Rubber products are frequently made up of several rubber layers each with a same or a different chemical composition. During this “build up,” the rubber layers must adhere to one another adequately in their pre-vulcanized state. For example, an assembled tire blank is required to hold together for a fairly long period prior to vulcanization. It is therefore important that the rubber mixtures used have an adequate “tack,” the force required to pull apart two pre-vulcanized rubber mixtures which have been pressed together under certain defined conditions. While natural rubber mixtures generally have good tackiness, mixtures of synthetic rubbers are much less tacky and, in extreme cases, possess no tackiness at all. Therefore, it has been common practice to add a tackifier to less tacky rubbers or rubber mixtures to increase their tack. In synthetic rubber products, synthetic rubber adhesive compositions are employed to improve tack and provide good cured adhesion. Moreover, the rubber composition must not only have good initial tack, but also remain sufficiently tacky during the manufacturing process (i.e., good tack retention), even when the process is interrupted for fairly long periods, which is not unusual, particularly when manufacturing involves processes at different locations or requires storage and/or transport of pre-finished goods.
However, during the manufacturing and processing of the base-modified alkylphenol-aldehyde resins, the molecular weight of the resins can increase, causing instability of the resins, which limits the usefulness of the resin in many applications. Typically, the base-modified alkylphenol-aldehyde resins need to further react with an epoxide or other chemical reagents to stabilize the basic moiety or other reactive moieties in the resins.
Therefore, there remains a continual need to develop tackifiers based on base-modified alkylphenol-aldehyde resins which not only provide increased tack and tack retention, but, at the same time, also provide an increased stability. This invention answers that need.